Victor Epoch, the host of the television science series "Astro", is distressed. A recent interview with Superman, regarding time travel, has deepened Epoch's feeling of mortality. Epoch is less concerned with actually dying than he is with missing out on the world's that's coming. In the hopes of catching just a glimpse of the future, Epoch begins an experiment, using a massive gyroscopic device, to recreate Superman's method of breaching the time barrier. Unbeknownst to Epoch, his experiment causes a piece of the future to displace the present, shunting that present into the past. Superman investigates the area of displacement, puzzling over the strange shift in eras that has taken place over a few block of Metropolis. Within that displaced zone, a pair of Tiger Men hunt for Kamandi, the Last Boy on Earth. The Tiger Men give up the hunt upon reaching the edge of the displacement zone, as the spectacle of present day Metropolis looms before them. Superman, investigating the perimeter of the displacement zone, as Clark Kent, is called back to the Daily Planet, by Jimmy Olsen. With his telescopic vision, Kent sees the Tiger Men abducting innocent citizens. Ditching Olsen, Kent, as Superman, races to their rescue.
Olsen makes it back to the Daily Planet building, just as it is shunted into the past, replaced by it's future counterpart. Kamandi is brought down by the Tiger Men, then brought before their ruler, Great Caesar. Superman intervenes on Kamandi's behalf. Superman quickly realizes that not only do the Tiger Men have nothing to do with the time displacement, but they are unaware of it's effect on their era. Instead, the Tiger Men believe that the human populace is encroaching on their territory, somehow having built the city that now surrounds them. Kamandi recognizes Superman from old videos he had been able to salvage. Believing that Kamandi may hold the answer to the time displacement, Superman carries the Last Boy On Earth away from the Tiger People. Epoch, having finally walked outside his laboratory, realizes that his experiment has gone awry. Before he can act, he is taken prisoner by the Tiger People. Kamandi explains how dire life is in his time, pleading with Superman to help him, and his people. Superman knows, though, that he cannot change history. The Tiger Men begin rounding up as many humans as they can find. Superman and Kamandi battle against the Tiger Men. In the melee, they become separated, leading to Kamandi's defeat at the overwhelming forces of the Tiger Men.
Deciding that he might learn more about the time displacement as a prisoner, Superman, as Clark Kent, allows himself to be arrested by the Tiger Men. Taken to a "kennel" for holding humans, Kent re-encounters Kamandi, as well as Epoch. Once Kent discovers that Epoch's experiment is the cause of the time displacement, he uses his super-strength, in a discreet fashion, to break out of the "kennel". Kent, as Superman, races to Epoch's laboratory, but falls prey to the ever expanding zone of temporal displacement. Superman finds himself in the distant past, arriving just in time to save the Daily Planet staff from a pack of Tyrannosaurs. Kamandi and Epoch are en route to Epoch's laboratory when, once again, Epoch is taken by the Tiger People. Epoch shouts out instructions to Kamandi for ending his experiment. Using every iota of power he possesses, Superman is finally able to break the time barrier and return to present day Metropolis. He arrives at Epoch's laboratory in time to keep Kamandi from being killed, by the stray bolts of radiation coming off the gyroscopic device. Following Kamandi's instructions, Superman shuts down Epoch's experiment. As the temporal displacement rights itself, Kamandi is drawn back to his proper era. Superman offers to take Epoch on a tour through time, but Epoch refuses. Terrified by what he's seen of the world that's coming, Epoch is content to live out his life in the present day.